The present invention relates to a resilient switch and, more particularly, to a resilient switch for communications systems, wireless communications systems using distributed antennas, and to cellular and radio distribution points.
The use of a switch matrix for wireless communications systems based on distributed antennas is disclosed by Motley et al. in U.S. Pat. No. 5,682,256. Motley uses a switch matrix to interconnect a number of base stations on the input ports to a number of distributed antennas on the output ports. The switch matrix allows any combination of inputs to be connected to any combination of outputs so that base stations can be connected to antennas in a very flexible manner. This allows wireless services such as cellular radio to be delivered to users with significant cost savings for network operators. The benefits of using a switched distributed antenna system are outlined for example in a recent paper by Wake and Beacham, Proc. SPIE vol. 5466, 2004.
FIG. 1 shows a switch matrix having an exemplary size of 8×4. The switch matrix comprises of 8 input ports 1 and 4 output ports 2. Each input port is connected to a 1:4 power splitter 3 and each output port is connected to an 8:1 power combiner 4. For each splitter 3, its four outputs are connected to the inputs of the four combiners 4 as shown in FIG. 1 so as to ensure that any input to the switch matrix can be available at any output of the switch matrix. Each connection 5 between a given splitter and a given combiner comprises a single pole single throw switch element 6 and a variable attenuator 7 in series. FIG. 1 schematically illustrates only one switch element 6 and one variable attenuator, but there are 32 switch elements and 32 variable attenuators in total for this size of matrix. The switches can be set to either an “on” state or an “off” state so that any combination of input signals can be routed to any combination of output ports. The variable attenuators can be set to balance the path loss across all paths between input and output.
The switch matrix of FIG. 1 is a single point of failure for a system such as described in Motley et al. If the switch matrix fails, there would be a loss of service between the network operators at one end of the switch matrix and users at the other end. Even if only a single connection 5 in the switch matrix fails, there will be a loss of service.